1. Field of the Invention
This invention relates to a recording and reproducing apparatus for recording main information consisting of a plurality of programs on a tape-shaped recording medium in the longitudinal direction of the medium and for reproducing the recorded- main information.
2. Description of the Related Art
In the field of magnetic recording, high density recording has recently come to be pursued. This trend has brought about, among others, a method of digitally recording an audio signal which is compressed in the directions of amplitude and time base thereof. In the case of a magnetic recording and reproducing apparatus of the rotary two-head helical scanning type (hereinafter referred to as a VTR), for example, a magnetic tape has generally been arranged to be wrapped at least 180 degrees round a rotary cylinder. Whereas, in accordance with this digital recording method, the tape is wrapped more than 180 (180 +) degrees including an extra wrapping part; and in this extra part is recorded an audio signal which is pulse code modulated (PCM) and time-base compressed.
FIG. 1 of the accompanying drawings shows a tape transport system of the above stated type VTR. FIG. 2 shows recording tracks formed on a magnetic tape by the VTR which is arranged as shown in FIG. 1.
Referring to FIGS. 1 and 2, the illustrations include a magnetic tape 1; a rotary cylinder 2; heads 3 and 4 which are mounted on the rotary cylinder 2 with a phase difference of 180 degrees between them and which have different azimuth angles; an area 5 within which a video signal is recorded in each of recording tracks formed on the magnetic tape 1 (hereinafter referred to as a video area); an area 6 within which an audio signal is recorded in each track (hereinafter referred to as an audio area). The video area 5 is formed with a portion of the magnetic tape which corresponds to a 180 degree wrapped portion of the whole circumference of the rotary cylinder 2 traced by the heads 3 and 4. The audio area 6 is formed with a portion of the tape corresponding to a .theta. degree portion of the circumference of the rotary cylinder 2 traced by the heads 3 and 4.
In accordance with another known method, a VTR of the above stated type is arranged to have an audio signal which differs from the audio signal recorded in the audio area 6 recorded also in the video area 5. More specifically, the method is based on the following concept: Assuming that the degree .theta. is 36.degree., five audio areas each of which is the same as the audio area 6 are obtainable in addition to the area 6. Then, in each of these audio areas, an audio signal can be recorded in a pulse code modulated (PCM) state. FIG. 3 shows a tape transport system of a recording and reproducing apparatus which is arranged to record and reproduce such multi-channel audio signals. FIG. 4 shows the recording tracks formed on a tape by the apparatus arranged as shown in FIG. 3.
In recording the PCM audio signal on a tape, the audio signal undergoes a non-linear compressing process while it is in an analog signal state. The compressed analog audio signal is band restricted to 0 to 1/2 sampling frequency (fs) by means of a low-pass filter. The band restricted audio signal is then converted into digital data of ten bits by means of an analog-to-digital (A/D) converter. The ten-bit data is non-linearly compressed into digital data of eight bits. The eight-bit data undergoes a series of error preventing processes including an interleave process, a CRCC process and a parity word adding process. The data is thus pulse code modulated and is then recorded on the magnetic tape. During reproduction, the PCM audio data thus recorded is taken out by means of a bit clock which is locked at data formed by a phase locked loop (PLL). The data thus taken out undergoes an error detecting CRCC process and an error correcting process by parity. The data is thus expanded from the eight-bit state to a ten-bit data. The ten-bit data is converted into an analog signal by means of a digital-to-analog (D/A) converter. The analog signal is then subjected to an analog expansion process carried out through a post-filter to become an audio signal.
FIG. 5 is a block diagram showing an arrangement for carrying out the signal processing operation described in the foregoing. Referring to FIG. 5, a block 11 is arranged to compress the incoming analog audio signal in the direction of amplitude of the signal. A pre-filter (LPF) 12 is arranged to impose a band restriction on the analog audio signal. An A/D converter 13 is arranged to A/D convert the signal into a ten-bit data. A block 14 is arranged to compress the ten-bit data into eight-bit data. A block 15 is arranged to add to the eight-bit data such redundant bits as a CRCC and a parity word. A block 16 is arranged to perform a PCM operation. The arrangement includes a memory 17; a magnetic recording and reproducing system 18; a PCM demodulation block 19; a memory 20; a block 21 arranged to perform error detecting and correcting processes and an interpolating process; a block 22 arranged to expand the eight-bit data into data of ten bits; a D/A converter 23; an LPF 24 which is a post-filter; a block 25 arranged to expand the analog signal produced from the LPF 24; and a clock pulse generator 26.
An example of a data format conventionally employed for an apparatus of the kind described above is arranged as follows: FIG. 6 shows the data format in which data is recorded within each track included in each of the areas shown in FIG. 4. More specifically, this is a data format containing PCM audio data corresponding to an audio signal for two-channels of 1/60 sec.
In the data matrix which is shown in FIG. 6, a column SYNC is for synchronizing data. A column ADDRESS is for address data. Columns P and Q are for redundant data. A column CRCC is for CRCC (cyclic redundancy check code) data which is well known. Each of columns Dl and D2 consists of a plurality of data columns. These data columns contain audio signal information of two channels. The data matrix includes rows b(0) to b(3x-1). Each of these rows forms one data block. The data of each data block are recorded one after another from the left-hand side to the right-hand side as viewed on the drawing. For example, after the data of the column SYNC in the row b(0) is recorded, the data of the column ADDRESS in the row b(0) is recorded. Then, the data of the column P in the row b(0) is recorded. Further, after the data of the last column in the row b(x) is recorded, the data of the column SYNC in the row b(x+1) is recorded. Data recording in one track comes to an end when the data of the last column in the row b(3x-1) is recorded.
In the first of the plurality of columns included in the column Dl, six data ID0 to ID5 in the rows b(0), b(1), b(x), b(x+1), b(2x), b(2x+1) represent additional information other than the audio signal information (hereinafter these six data are referred to as ID data).
The multi-channel PCM audio signal recording and reproducing apparatus readily permits audio signal recording over a period of 90 minutes and thus permits recording for nine hours on a single tape. However, the result of such recording necessitates a long period of time in finding what is recorded where on the tape. To solve this problem, it has been contrived to generate ID data specially for facilitating a look-up operation when the data corresponding to the audio signal is recorded and to record the generated ID data in a specific position within each of recording tracks on the tape. An example of the look-up ID data has been disclosed in U.S. Pat. Application Serial No. 816,425, filed by the present applicant. It is conceivable to provide such look-up ID data, for example, by setting a flag at a part corresponding to a blank (mute) part between one program and another or by recording a program number for each of the programs.
However, with the ID data arranged in that manner, in detecting the flag between the programs or in detecting the program number, the rotary head might come to trace a wrong track which is oppositely azimuth recorded on the recording medium or tape. Therefore, it is not always possible to detect a change-over part between programs or the leader part of a program by one tracing action of the head. Further, if an attempt is made to shorten the length of time required for look-up by increasing the travelling speed of the tape during a look-up operation, it generally becomes impossible to accurately detect the look-up ID data. Besides, the tape cannot be always brought to a stop at a desired point due to the force of inertia.